A substrate on which electronic components are mounted deforms due to heat and load applied during a manufacturing process, and the substrate does not necessarily maintain a shape according to design dimensions at a time the electronic components are mounted. For this reason, apparatuses for mounting electronic components are designed to make a positional correction of a mounting position for each of the electronic components on the substrate by detecting an identification mark that is originally formed on the substrate for positional identification. In the past, according to one known method, two or three identification marks are placed on the substrate, and they are observed by a camera in order to determine mounting positions.
The method of observing two positions is effective only for a deformation of the substrate that expands or contracts uniformly both in length and width. The method of observing three positions, on the other hand, resolves the above shortcoming and is effective even if the substrate is deformed in different ratios of expansion and contraction between the length and the width. However, all of the above-described deformations are limited to a case in which a rectangular substrate maintains its rectangular shape even after deformation. Therefore, the method of observing three positions is unable to provide, with a required accuracy, for an ordinary irregular deformation in which a ratio of expansion and contraction of the substrate is not uniform and is different in part, for example in cases where the deformation is from a rectangular shape to a trapezoidal shape. Thus, there exists a problem with the prior art apparatuses in that they are unable to make a positional correction using the positional identification marks when mounting electronic components, in the case where the substrate is deformed in an irregular manner.